A touch panel is used as a pointing device to input instructions about icons and the like displayed on a display of an electronic apparatus. Depending on the method for detecting an input operation position, touch panels of various detection types have been known. Examples thereof include a capacitive type, a resistive film type, and an optical type. A resistive touch panel includes a resistive coating having a uniform resistance per unit length, arranged along an input operation surface. Distances between detection electrodes and an input operation position are identified from resistances therebetween, whereby the input operation position is detected.
In order for the resistive touch panel to make the display installed on the rear side viewable, the detection electrodes and the resistive film arranged on the surface or backside of the input operation surface need to be made of expensive transparent materials. Since transparent materials themselves have a limited transmittance, there is a problem that the display becomes less viewable through the touch panel.
A capacitive touch panel utilizes the fact that an input operation increases the stray capacitance of a detection electrode or electrodes that the input operation member approaches (the capacitances between the input operation member and the detection electrodes). The capacitive touch panel detects an input operation position on an input operation surface where detection electrodes are arranged, on the basis of a change in capacitance between the input operation member and the detection electrodes. For example, a known conventional capacitive touch panel includes a large number of X-side detection electrodes and Y-side detection electrodes which are formed in a matrix configuration to intersect each other on the surface and backside of an insulating substrate. The capacitive touch panel detects the input operation position of the input operation member such as a finger on the basis of the arrangement positions of X- and Y-side detection electrodes of which the capacitances increase near the location where the input operation member approaches (see Patent Literature 1).
The change in capacitance resulting from the approach of the input operation member to a specific detection electrode is small and inversely proportional to the distance between the input operation member and the detection electrode. In the capacitive touch panel according to Patent Literature 1, the large number of X- and Y-side detection elements for detecting a change in capacitance are arranged close to the input operation area near input operation positions. In order for the display on the rear side to be viewable, such detection electrodes are made of a transparent material. Like the resistive touch panel, there is the problem that the cost is high and the transmittance decreases to make the display less viewable.
An optical touch panel includes a plurality of pairs of light emitting elements and light receiving elements which are arranged around an input operation surface to form a grid of optical paths over the input operation surface. The input operation position is detected on the basis of the arrangement positions of pairs of light emitting and receiving elements of which the optical paths are blocked by the input operation. In such an optical touch panel, the detection elements for detecting the input operation position are arranged around the input operation surface. The surface of a transparent plate such as a glass substrate can thus be used as the input operation area, so that input operations can be made while viewing the display on the rear side through the transparent plate.